Structure And Property Research For Polyethylene Subjected To Vibration Excitation Based On Molecular Dynamics Simulation

With wide application of the polymer material in many fields, higher mechanical properties are required for polymers. The appearance of dynamic molding technology brings a new way to improve the properties of the polymer, but its impact mechanism on the products remains to be further explored. Research on the impact of external excitation towards polymer’s structure and properties at molecular scale has important theoretical significance. Based on this, this paper develops a new non-equilibrium molecular dynamics simulation method named as vibration excitation molecular dynamics (VEMD) to investigate the effects of external excitation field to the polyethylene folding, multi-chain polyethylene’s structure and mechanical properties. The whole paper can be divided into three parts:Firstly, the folding behavior of a single-chain polyethylene under external excitation is simulated using molecular dynamic simulation method to study the impact of external excitation on polyethylene molecule folding structure. The simulation results show that the vibration excitation has a significant influence to some structure parameters such as the polyethylene molecule’s surface area, the stability of the structure, the dihedral angle distribution, the mode of vibration and the radius of gyration. In addition, frequency and amplitude determine the way and the extent of the affects, and the frequency plays a key role in the simulation.Secondly, the initial polyethylene conformation model with8chains and4000monomers is built up. The generation of the initial polymer conformation is the most complex and important process in building up a polymer molecule model. In this paper we build the ideal initial multi-chain polyethylene model based on the compression method.Finally, the vibration excitation simulation is introduced into the initial multi-chain conformation of polyethylene. Based on this, the influence of the external excitation on the mechanical properties and condensed matter configuration of the polyethylene is studied. The simulation results show that the structure’s entanglements decrease with the introduction of the external excitation. At room temperature the mechanical strength of the polymer structure is also be significantly affected by the external excitation. Different frequencies and amplitudes have different effects on the polyethylene’s structures and properties.This work is supported by the national key basic research program project "polymer molding process and mold design optimization"(No.2012CB025905).